A polarimetry technique based on stack targets and beta-gamma-coincidences has been applied to th... more A polarimetry technique based on stack targets and beta-gamma-coincidences has been applied to the N-16 nuclei produced in the ground state capture of negative muons on O-16 nuclei. The performance of the polarimeter and the first measurements of beta-asymmetry due to the longitudinal nuclear polarization are discussed.
Stochastic processes are highly relevant in research fields as different as neuroscience, economy... more Stochastic processes are highly relevant in research fields as different as neuroscience, economy, ecology, chemistry, and fundamental physics. However, due to their intrinsic unpredictability, stochastic mechanisms are very challenging for any kind of investigations and practical applications. Here we report the deliberate use of stochastic X-ray pulses in two-dimensional spectroscopy to the simultaneous mapping of unoccupied and occupied electronic states of atoms in a regime where the opacity and transparency properties of matter are subject to the incident intensity and photon energy. A readily transferable matrix formalism is presented to extract the electronic states from a dataset measured with the monitored input from a stochastic excitation source. The presented formalism enables investigations of the response of the electronic structure to irradiation with intense X-ray pulses while the time structure of the incident pulses is preserved.
The accurate measurement of the arrival time of a hard x-ray free electron laser (FEL) pulse with... more The accurate measurement of the arrival time of a hard x-ray free electron laser (FEL) pulse with respect to a laser is of utmost importance for pump-probe experiments proposed or carried out at FEL facilities around the world. This paper presents the latest device to meet this challenge, a THz streak camera, and discusses the challenges in its design, use, and analysis of results.
We describe the``Surface/Interface: Microscopy'' beamline currently under construction at the Pau... more We describe the``Surface/Interface: Microscopy'' beamline currently under construction at the Paul Scherrer Institut. This beamline will use a photoemission electron microscope to study the electronic and magnetic structure of materials. Its photon energy range will be 94±2000 eV. To allow time resolved measurements with millisecond resolution we use a new scheme allowing to switch the photon helicity optically without perturbing the electron orbit. Two identical elliptical insertion devices are placed behind each other in the same straight section. They can produce light with opposing helicities. These two sources are separated horizontally by introducing a small static parallel oset in the electron orbit. Switching between the two rays of opposite helicities is done mechanically at the horizontal focus behind the monochromator. The two sources are brought to overlap on the sample by slightly defocussing the refocussing mirror. A commercial microscope (Dx $ 20 nm resolution) is adapted to the synchrotron by various upgrades. These include a software combining microscope and beamline control, a computer controlled mechanical alignment system, a separate sample preparation chamber, and sample cooling using liquid nitrogen. The beamline will be available for user operation in 2002.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2001
The insertion devices under construction for phase I of the Swiss Light Source (SLS) are describe... more The insertion devices under construction for phase I of the Swiss Light Source (SLS) are described. Five undulators and one wiggler will be installed in four straight sections of the third generation 2:4 GeV SLS storage ring, under construction at the Paul Scherrer Institute. To provide undulator radiation in the energy range from 10 eV to 18 keV, both long period and short period, small gap undulators will be installed.
The SwissFEL X-ray Free Electron Laser (XFEL) facility started construction at the Paul Scherrer ... more The SwissFEL X-ray Free Electron Laser (XFEL) facility started construction at the Paul Scherrer Institute (Villigen, Switzerland) in 2013 and will be ready to accept its first users in 2018 on the Aramis hard X-ray branch. In the following sections we will summarize the various aspects of the project, including the design of the soft and hard X-ray branches of the accelerator, the results of SwissFEL performance simulations, details of the photon beamlines and experimental stations, and our first commissioning results.
19th International Conference on Ultrafast Phenomena, 2014
ABSTRACT We have performed time-resolved resonant X-ray emission spectroscopy after UV photoexcit... more ABSTRACT We have performed time-resolved resonant X-ray emission spectroscopy after UV photoexcitation of a colloidal solution of ZnO nanoparticles. The results point to electron trapping sites located at oxygen vacancies in the lattice.
ABSTRACT We present our new results exploiting simultaneously picosecond and femtosecond x-ray em... more ABSTRACT We present our new results exploiting simultaneously picosecond and femtosecond x-ray emission spectra in concert with x-ray diffuse scattering patterns, which provide complementary information to x-ray absorption studies. Key systems presented include a photocatalytic compound.
The two-color operation of free electron laser (FEL) facilities allows the delivery of two FEL pu... more The two-color operation of free electron laser (FEL) facilities allows the delivery of two FEL pulses with different energies, which opens new possibilities for user experiments. Measuring the arrival time of both FEL pulses relative to the external experimental laser and to each other improves the temporal resolution of the experiments using the two-color FEL beam and helps to monitor the performance of the machine itself. This work reports on the first simultaneous measurement of the arrival times of two hard X-ray FEL pulses with the THz streak camera. Measuring the arrival time of the two FEL pulses, the relative delay between them was calculated and compared to the set values. Furthermore, we present the first comparison of the THz streak camera method to the method of FEL induced transient transmission. The results indicate a good agreement between the two methods.
The SwissFEL soft X-ray free-electron laser (FEL) beamline Athos will be ready for user operation... more The SwissFEL soft X-ray free-electron laser (FEL) beamline Athos will be ready for user operation in 2021. Its design includes a novel layout of alternating magnetic chicanes and short undulator segments. Together with the APPLE X architecture of undulators, the Athos branch can be operated in different modes producing FEL beams with unique characteristics ranging from attosecond pulse length to high-power modes. Further space has been reserved for upgrades including modulators and an external seeding laser for better timing control. All of these schemes rely on state-of-the-art technologies described in this overview. The optical transport line distributing the FEL beam to the experimental stations was designed with the whole range of beam parameters in mind. Currently two experimental stations, one for condensed matter and quantum materials research and a second one for atomic, molecular and optical physics, chemical sciences and ultrafast single-particle imaging, are being laid o...
Dear colleagues, An important milestone for the realiza7on of the new SwissFEL facility was reach... more Dear colleagues, An important milestone for the realiza7on of the new SwissFEL facility was reached on the ?@th of August ?ABA, when the core of the new facility, the ?CA MeV injector, was set into opera7on at the Paul Scherrer Ins7tute. This part will be used to develop and test new schemes in accelerator physics as well as diagnos7cs and undulators. The SwissFEL facility is expected to start user opera7on in ?ABN. It is already evident that the experiments performed at FLASH (Hamburg) and LCLS (Stanford) will enable discoveries in many areas of current research that cannot be obtained using exis7ng methods. For this reason the SwissFEL Photonics Group is now developing novel measurement methods for use with the X-ray free electron laser. These include a) a demonstra7on of ultrafast ini7a7on of chemical reac7ons using high-energy pulses of terahertz radia7on – for future THz pump / XFEL probe experiments, and b) exploi7ng correlated scaWering to determine the structure of biomolecu...
Acta Crystallographica Section A Foundations and Advances, 2014
X-ray free-electron laser (XFEL) sources create X-ray pulses of unprecedented brilliance and open... more X-ray free-electron laser (XFEL) sources create X-ray pulses of unprecedented brilliance and open up new possibilities for the structural characterization of crystalline materials. By exposing a small crystallite (100nm-10μm) to a single ultrafast pulse, a diffraction pattern can be obtained before the crystal is damaged. If such single-pulse diffraction patterns, collected sequentially on many randomly oriented crystallites, are combined, it is possible to determine the structure of the material accurately [1]. One of the drawbacks of this approach is that only a single position of the Ewald sphere is accessed in each pattern, so, because reflections have a finite width, the diffraction condition is not satisfied completely for any of the reflections recorded. The new XFEL source that is being developed in Switzerland (SwissFEL) will provide a broad-bandpass mode with an energy bandwidth of about 4% [2]. By using the full energy range of the SwissFEL beam, a new option for structur...
The sixth conference on the intersections of particle and nuclear physcis, 1997
A new experimental search for muonium-antimuonium conversion was conducted at the Paul Scherrer I... more A new experimental search for muonium-antimuonium conversion was conducted at the Paul Scherrer Institute, Villigen, Switzerland. The preliminary analysis yielded one event fulfilling all required criteria at an expected background of 1.7(2) events due to accidental coincidences. An upper limit for the conversion probability in 0.1 T magnetic field is extracted as 8 • 10 −11 (90% CL).
Inner structures of composite materials, components or tissues have to be characterised with micr... more Inner structures of composite materials, components or tissues have to be characterised with micrometer and even submicrometer resolution. It is often highly desirable that specimens stay unchanged after a first characterization to allow meaningful subsequent tests. This justifies major efforts for an ongoing improvement of nondestructive radiographical and tomographical methods for morphological characterization. Radiography and tomography as well as laminography can fulfill these requirements. X-ray sources and detectors have been improved. This applies for synchrotron-beamline systems as well as for tube based systems. A novel detector concept has been implemented in the XTM station at the SLS of the PSI in Villigen, Switzerland. This microtomography station at the SLS has started its operation in spring 2002. A selection of results related to industrial and scientific applications is presented in this contribution. Special emphasis will be given to first results of tomography with limited numbers of projections which is comparable to laminography. This method allows to characterise e.g. ribbons of tissue under load.
Advances in X-ray Free-Electron Lasers Instrumentation III, 2015
SwissFEL is the Free Electron Laser (FEL) facility under construction at the Paul Scherrer instit... more SwissFEL is the Free Electron Laser (FEL) facility under construction at the Paul Scherrer institute (PSI), aiming to provide users with X-ray pulses of lengths down to 2 femtoseconds at standard operation. The measurement of the length of the FEL pulses and their arrival time relative to the experimental laser is crucial for the pump-probe experiments carried out in such facilities. This work presents a new device that measures hard X-ray FEL pulses based on the THz streak camera concept. It describes the prototype setup called pulse arrival and length monitor (PALM) developed at PSI and tested in Spring-8 Angstrom Compact Free Electron Laser (SACLA) in Japan. Based on the first results obtained from the measurements, we introduce the new improved design of the second generation PALM setup that is currently under construction and will be used in SwissFEL photon diagnostics.
This article describes a state-of-the-art hard X-ray beamline for materials science at a third-ge... more This article describes a state-of-the-art hard X-ray beamline for materials science at a third-generation synchrotron light source presently being commissioned in Switzerland, together with two typical pieces of experimental work for which the beamline is being optimized. After a discussion of the motivation, photon source, optics and experimental stations of the beam line, we present the results of some X-ray scattering studies of order–disorder phenomena that were recently performed at other synchrotron radiation sources (HASYLAB, Hamburg, and ESRF, Grenoble). The phenomena to be discussed are spontaneous ordering in epitaxial AlxGa1-xAs films and confinement-induced ordering of colloidal solutions.
The accurate measurement of the arrival time of a hard x-ray free electron laser (FEL) pulse with... more The accurate measurement of the arrival time of a hard x-ray free electron laser (FEL) pulse with respect to a laser is of utmost importance for pump-probe experiments proposed or carried out at FEL facilities around the world. This manuscript presents the Photon Arrival and Length Monitor (PALM), the latest device to meet this challenge, a THz streak camera, and discusses the challenges in its design, use, and analysis of results.
A polarimetry technique based on stack targets and beta-gamma-coincidences has been applied to th... more A polarimetry technique based on stack targets and beta-gamma-coincidences has been applied to the N-16 nuclei produced in the ground state capture of negative muons on O-16 nuclei. The performance of the polarimeter and the first measurements of beta-asymmetry due to the longitudinal nuclear polarization are discussed.
Stochastic processes are highly relevant in research fields as different as neuroscience, economy... more Stochastic processes are highly relevant in research fields as different as neuroscience, economy, ecology, chemistry, and fundamental physics. However, due to their intrinsic unpredictability, stochastic mechanisms are very challenging for any kind of investigations and practical applications. Here we report the deliberate use of stochastic X-ray pulses in two-dimensional spectroscopy to the simultaneous mapping of unoccupied and occupied electronic states of atoms in a regime where the opacity and transparency properties of matter are subject to the incident intensity and photon energy. A readily transferable matrix formalism is presented to extract the electronic states from a dataset measured with the monitored input from a stochastic excitation source. The presented formalism enables investigations of the response of the electronic structure to irradiation with intense X-ray pulses while the time structure of the incident pulses is preserved.
The accurate measurement of the arrival time of a hard x-ray free electron laser (FEL) pulse with... more The accurate measurement of the arrival time of a hard x-ray free electron laser (FEL) pulse with respect to a laser is of utmost importance for pump-probe experiments proposed or carried out at FEL facilities around the world. This paper presents the latest device to meet this challenge, a THz streak camera, and discusses the challenges in its design, use, and analysis of results.
We describe the``Surface/Interface: Microscopy'' beamline currently under construction at the Pau... more We describe the``Surface/Interface: Microscopy'' beamline currently under construction at the Paul Scherrer Institut. This beamline will use a photoemission electron microscope to study the electronic and magnetic structure of materials. Its photon energy range will be 94±2000 eV. To allow time resolved measurements with millisecond resolution we use a new scheme allowing to switch the photon helicity optically without perturbing the electron orbit. Two identical elliptical insertion devices are placed behind each other in the same straight section. They can produce light with opposing helicities. These two sources are separated horizontally by introducing a small static parallel oset in the electron orbit. Switching between the two rays of opposite helicities is done mechanically at the horizontal focus behind the monochromator. The two sources are brought to overlap on the sample by slightly defocussing the refocussing mirror. A commercial microscope (Dx $ 20 nm resolution) is adapted to the synchrotron by various upgrades. These include a software combining microscope and beamline control, a computer controlled mechanical alignment system, a separate sample preparation chamber, and sample cooling using liquid nitrogen. The beamline will be available for user operation in 2002.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2001
The insertion devices under construction for phase I of the Swiss Light Source (SLS) are describe... more The insertion devices under construction for phase I of the Swiss Light Source (SLS) are described. Five undulators and one wiggler will be installed in four straight sections of the third generation 2:4 GeV SLS storage ring, under construction at the Paul Scherrer Institute. To provide undulator radiation in the energy range from 10 eV to 18 keV, both long period and short period, small gap undulators will be installed.
The SwissFEL X-ray Free Electron Laser (XFEL) facility started construction at the Paul Scherrer ... more The SwissFEL X-ray Free Electron Laser (XFEL) facility started construction at the Paul Scherrer Institute (Villigen, Switzerland) in 2013 and will be ready to accept its first users in 2018 on the Aramis hard X-ray branch. In the following sections we will summarize the various aspects of the project, including the design of the soft and hard X-ray branches of the accelerator, the results of SwissFEL performance simulations, details of the photon beamlines and experimental stations, and our first commissioning results.
19th International Conference on Ultrafast Phenomena, 2014
ABSTRACT We have performed time-resolved resonant X-ray emission spectroscopy after UV photoexcit... more ABSTRACT We have performed time-resolved resonant X-ray emission spectroscopy after UV photoexcitation of a colloidal solution of ZnO nanoparticles. The results point to electron trapping sites located at oxygen vacancies in the lattice.
ABSTRACT We present our new results exploiting simultaneously picosecond and femtosecond x-ray em... more ABSTRACT We present our new results exploiting simultaneously picosecond and femtosecond x-ray emission spectra in concert with x-ray diffuse scattering patterns, which provide complementary information to x-ray absorption studies. Key systems presented include a photocatalytic compound.
The two-color operation of free electron laser (FEL) facilities allows the delivery of two FEL pu... more The two-color operation of free electron laser (FEL) facilities allows the delivery of two FEL pulses with different energies, which opens new possibilities for user experiments. Measuring the arrival time of both FEL pulses relative to the external experimental laser and to each other improves the temporal resolution of the experiments using the two-color FEL beam and helps to monitor the performance of the machine itself. This work reports on the first simultaneous measurement of the arrival times of two hard X-ray FEL pulses with the THz streak camera. Measuring the arrival time of the two FEL pulses, the relative delay between them was calculated and compared to the set values. Furthermore, we present the first comparison of the THz streak camera method to the method of FEL induced transient transmission. The results indicate a good agreement between the two methods.
The SwissFEL soft X-ray free-electron laser (FEL) beamline Athos will be ready for user operation... more The SwissFEL soft X-ray free-electron laser (FEL) beamline Athos will be ready for user operation in 2021. Its design includes a novel layout of alternating magnetic chicanes and short undulator segments. Together with the APPLE X architecture of undulators, the Athos branch can be operated in different modes producing FEL beams with unique characteristics ranging from attosecond pulse length to high-power modes. Further space has been reserved for upgrades including modulators and an external seeding laser for better timing control. All of these schemes rely on state-of-the-art technologies described in this overview. The optical transport line distributing the FEL beam to the experimental stations was designed with the whole range of beam parameters in mind. Currently two experimental stations, one for condensed matter and quantum materials research and a second one for atomic, molecular and optical physics, chemical sciences and ultrafast single-particle imaging, are being laid o...
Dear colleagues, An important milestone for the realiza7on of the new SwissFEL facility was reach... more Dear colleagues, An important milestone for the realiza7on of the new SwissFEL facility was reached on the ?@th of August ?ABA, when the core of the new facility, the ?CA MeV injector, was set into opera7on at the Paul Scherrer Ins7tute. This part will be used to develop and test new schemes in accelerator physics as well as diagnos7cs and undulators. The SwissFEL facility is expected to start user opera7on in ?ABN. It is already evident that the experiments performed at FLASH (Hamburg) and LCLS (Stanford) will enable discoveries in many areas of current research that cannot be obtained using exis7ng methods. For this reason the SwissFEL Photonics Group is now developing novel measurement methods for use with the X-ray free electron laser. These include a) a demonstra7on of ultrafast ini7a7on of chemical reac7ons using high-energy pulses of terahertz radia7on – for future THz pump / XFEL probe experiments, and b) exploi7ng correlated scaWering to determine the structure of biomolecu...
Acta Crystallographica Section A Foundations and Advances, 2014
X-ray free-electron laser (XFEL) sources create X-ray pulses of unprecedented brilliance and open... more X-ray free-electron laser (XFEL) sources create X-ray pulses of unprecedented brilliance and open up new possibilities for the structural characterization of crystalline materials. By exposing a small crystallite (100nm-10μm) to a single ultrafast pulse, a diffraction pattern can be obtained before the crystal is damaged. If such single-pulse diffraction patterns, collected sequentially on many randomly oriented crystallites, are combined, it is possible to determine the structure of the material accurately [1]. One of the drawbacks of this approach is that only a single position of the Ewald sphere is accessed in each pattern, so, because reflections have a finite width, the diffraction condition is not satisfied completely for any of the reflections recorded. The new XFEL source that is being developed in Switzerland (SwissFEL) will provide a broad-bandpass mode with an energy bandwidth of about 4% [2]. By using the full energy range of the SwissFEL beam, a new option for structur...
The sixth conference on the intersections of particle and nuclear physcis, 1997
A new experimental search for muonium-antimuonium conversion was conducted at the Paul Scherrer I... more A new experimental search for muonium-antimuonium conversion was conducted at the Paul Scherrer Institute, Villigen, Switzerland. The preliminary analysis yielded one event fulfilling all required criteria at an expected background of 1.7(2) events due to accidental coincidences. An upper limit for the conversion probability in 0.1 T magnetic field is extracted as 8 • 10 −11 (90% CL).
Inner structures of composite materials, components or tissues have to be characterised with micr... more Inner structures of composite materials, components or tissues have to be characterised with micrometer and even submicrometer resolution. It is often highly desirable that specimens stay unchanged after a first characterization to allow meaningful subsequent tests. This justifies major efforts for an ongoing improvement of nondestructive radiographical and tomographical methods for morphological characterization. Radiography and tomography as well as laminography can fulfill these requirements. X-ray sources and detectors have been improved. This applies for synchrotron-beamline systems as well as for tube based systems. A novel detector concept has been implemented in the XTM station at the SLS of the PSI in Villigen, Switzerland. This microtomography station at the SLS has started its operation in spring 2002. A selection of results related to industrial and scientific applications is presented in this contribution. Special emphasis will be given to first results of tomography with limited numbers of projections which is comparable to laminography. This method allows to characterise e.g. ribbons of tissue under load.
Advances in X-ray Free-Electron Lasers Instrumentation III, 2015
SwissFEL is the Free Electron Laser (FEL) facility under construction at the Paul Scherrer instit... more SwissFEL is the Free Electron Laser (FEL) facility under construction at the Paul Scherrer institute (PSI), aiming to provide users with X-ray pulses of lengths down to 2 femtoseconds at standard operation. The measurement of the length of the FEL pulses and their arrival time relative to the experimental laser is crucial for the pump-probe experiments carried out in such facilities. This work presents a new device that measures hard X-ray FEL pulses based on the THz streak camera concept. It describes the prototype setup called pulse arrival and length monitor (PALM) developed at PSI and tested in Spring-8 Angstrom Compact Free Electron Laser (SACLA) in Japan. Based on the first results obtained from the measurements, we introduce the new improved design of the second generation PALM setup that is currently under construction and will be used in SwissFEL photon diagnostics.
This article describes a state-of-the-art hard X-ray beamline for materials science at a third-ge... more This article describes a state-of-the-art hard X-ray beamline for materials science at a third-generation synchrotron light source presently being commissioned in Switzerland, together with two typical pieces of experimental work for which the beamline is being optimized. After a discussion of the motivation, photon source, optics and experimental stations of the beam line, we present the results of some X-ray scattering studies of order–disorder phenomena that were recently performed at other synchrotron radiation sources (HASYLAB, Hamburg, and ESRF, Grenoble). The phenomena to be discussed are spontaneous ordering in epitaxial AlxGa1-xAs films and confinement-induced ordering of colloidal solutions.
The accurate measurement of the arrival time of a hard x-ray free electron laser (FEL) pulse with... more The accurate measurement of the arrival time of a hard x-ray free electron laser (FEL) pulse with respect to a laser is of utmost importance for pump-probe experiments proposed or carried out at FEL facilities around the world. This manuscript presents the Photon Arrival and Length Monitor (PALM), the latest device to meet this challenge, a THz streak camera, and discusses the challenges in its design, use, and analysis of results.
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Papers by Rafael Abela